Many line-scan remote sensing sensors utilize multiple stages of time delay and integration to enhance the final image signal-to-noise ratio. The swath width of these systems can be limited by optical distortion, which causes nonlinear image scanning and results in image smear at the edge of the field-of-view (FOV). This can also result in both along- (or vertical direction) and cross-track (or horizontal direction) image smear and degraded image quality at the swath edges. As such, image distortion can be inherent to the optical design of an imaging system. In other cases, image distortion can be caused by many factors, such as atmospheric turbulence, mechanical vibrations, or mechanical translations and articulations in sensor systems.
Some conventional systems have employed limiting the field of view or, in some cases, slightly shifting charges in the focal plane arrays to account for the distortion. Other conventional solutions have included revising the optical design of the imaging system. However, these conventional solutions increase the number of mechanical components, mechanical translations and cost of the overall system.
Conventional linear arrays of single-cell charge-coupled device (CCD) detectors can be used to linearly scan along a single axis to produce a digital image. Scanning takes place in a single direction where each line of information is captured, stored, and amplified. An ideal line-scan remote sensing system has the optical image scanned uniformly across a focal plane in the along-track direction. Thus, three-phase charge-coupled devices (CCD) can only shift pixel charges along one direction (i.e., the along-track direction). As such, there exists a need to shift pixel charges in multiple directions during image integration.